1. Field of the Invention
The present invention relates to a path connection control system and control method thereof in a code division multiple access (CDMA) mobile communication system.
2. Description of the Related Art
It has been well known a mobile communication system, in which a mobile communication switching center is connected to a based station control unit through a wire circuit, a plurality of radio base stations are connected to the base station control unit through a wire circuit, and each base station is connected to a plurality of mobile terminals entering into a service area of an own station through radio circuits.
As a method for multiplexing radio communication paths in the mobile communication system, there has been known a code division multiple access (CDMA), in which information bit desired to communicate is multiplexed by spreading spectrum with several tens to several thousands bits of spreading code pattern, in addition to a frequency division multiple access (FDMA) or time division multiple access (TDMA).
CDMA is advantageous in strength against narrow barrage jamming and in capability of accommodating a plurality of paths within the same carrier wave. In current typical CDMA mobile communication system, a path connection system to establish a multiple paths for a plurality of radio base stations depending upon a condition of communication in call through one radio channel, has been employed. However, since CDMA uses a frequency band of low power in wide band, if number of paths is in excess of a certain number, radio signals arriving through such relatively large number of paths become mere noise. Therefore, connection control of the paths depending upon communication environment is particularly important in the CDMA mobile communication system.
FIG. 8 is an illustration for explaining path connection control of the conventional CDMA mobile communication system of this type.
In FIG. 8, the reference numeral 50 denotes mobile terminal (MS), 51 to 53 denote radio base stations (BTS), 54 denote a base station control unit (BSC), 58 denotes a mobile communication switching center (MSC).
On the other hand, in the base station control unit 54, the reference numeral 55 denotes a field intensity data extracting portion for extracting data of electric field intensity, 56 denotes a field intensity level monitoring portion for monitoring a field intensity level of the each radio base station based on the field intensity data, and 57 denotes a path setting control portion for determining path to be connected and path to be cut based on information from the field intensity level monitoring portion 56.
Next, path connection control of the CDMA mobile communication system shown in FIG. 8 will be discussed hereinafter.
Upon calling from the mobile terminal 50, a received field intensity of a pilot pattern transmitted from each radio base station 51 to 53 is measured in the mobile terminal 50 to establish call connection to the radio base station having the highest field intensity.
Here, it is assumed that the radio station having the highest field intensity is the radio base station 52, the radio terminal 50 at first establishes a path to the radio mobile station 52.
Even after establishing the path with the radio base station 52, the mobile terminal 50 continues measurement of the received field intensity of the pilot pattern to sequentially report information of measured field intensity of each radio base station to the base station control unit 54 through the path established with the radio base station 52.
In the base station control unit 54, data relating to the field intensity of each radio base station is extracted from the signal input from the radio base station 52 to feed the extracted data to the field intensity level monitoring portion 56 for monitoring the field intensity level of each radio base station in the field intensity level monitoring portion 56.
In hand off control while moving, when radio base station having field intensity level exceeding a threshold value to be a reference in establishing the path, newly appears, path is newly established to the newly appearing radio base station. Conversely, when the field intensity level of the radio base station, to which the path has already been established, is lowered to be lower than the threshold level to be the reference, the path to such radio base station is cut off.
Namely, in hand-off control in the conventional CDMA mobile communication system, path connection control is performed depending upon the actual field intensity level of each radio base station reported from the mobile terminal.
In the path connection control system in the conventional CDMA mobile communication system set forth above, since the path connection control is performed depending upon the actual field intensity level of each radio base station reported from the mobile terminal, the following problem is encountered.
At first, in order to re-establish paths depending upon high and low of actual field intensity level, hand-off control may cause delay when the mobile terminal is in motion at high speed to cause degradation of communication quality until completion of hand-off control.
Secondly, since path is uniformly established for the radio base stations having the field intensity level higher than or equal to the given level, the path is inherently established even for the radio base station temporarily passed through in a moment. On the other hand, in order to adapt to abrupt variation of communication environment, it becomes necessary to constantly establish a plurality of paths to waste communication resource.
It should be noted that, in Japanese Unexamined Patent Publication No. Heisei 7-322336, for xe2x80x9cHand-Off System for Cellular Telephone Systemxe2x80x9d, as shown in FIGS. 9, 10A and 10B, a position detector 518 for detecting a current position and traveling direction of the mobile terminal is provided in the mobile terminal 50, and a map data storage portion 522 for storing map data covering all cell area of the cellular phone system, a mobile terminal position information storage portion 521 for storing position information and traveling direction information detected by the position detector 518 and a mobile terminal traveling direction judgment portion 523 are provided in a control station 502.
The mobile terminal traveling direction judgment portion 523 detects the cell area where the mobile terminal moves with reference to the map data on the basis of the position information and traveling direction information when degradation of field intensity associating with movement of the mobile terminal is noticed to the mobile base station of the cell area where the mobile terminal is actually present.
The system disclosed in the above-identified publication has the radio base station map to perform hand-off after narrowing down the radio base stations to hand-off on the basis of traveling direction of the mobile terminal for effectively use a part of communication resource. However, even in this technology, the foregoing problem of delay in hand-off control during high speed travel cannot be resolved and effectiveness of use of communication resource is not satisfactory.
The present invention has been worked out in view of the drawbacks in the prior art set forth above. Therefore, it is an object of the present invention to provide a path connection control system and control method thereof in a CDMA mobile communication system which can establish minimum but sufficient paths without causing degradation of communication quality due to delay of hand off control even during high speed travel.
According to the first aspect of the present invention, a path connection control system in a CDMA mobile communication system for determining a radio base station to establish a path for communication with a mobile terminal by a base station control unit, the base station control unit comprises:
means for repeatedly inputting position information of the mobile terminal;
means for deriving a current position, a traveling speed and a traveling direction of the mobile terminal on the basis of repeatedly input position information of the mobile terminal;
a necessary path number map of predetermining necessary path number on the basis of a contour map,
the base station control unit performing control for deriving necessary paths with taking information of current position, traveling speed and traveling direction of the mobile terminal and information from the necessary path number map and determining radio base stations to establish paths.
According to the second aspect of the present invention, a path connection control system in a CDMA mobile communication system for determining a radio base station to establish a path for communication with a mobile terminal by a base station control unit, the base station control unit comprises:
means for repeatedly inputting position information of the mobile terminal;
means for deriving current position, traveling speed and traveling direction of the mobile terminal based on repeatedly input position information of the mobile terminal, and predicting position, traveling speed and traveling direction of the mobile terminal in the near future;
a necessary path number map of predetermining necessary path number on the basis of a contour map,
the base station control unit performing control for deriving necessary paths in the near further with taking information of current position, traveling speed and traveling direction of the mobile terminal, predicted information of position, traveling speed and traveling direction of the mobile terminal in the near future and information from the necessary path number map and determining radio base stations to establish paths.
According to the third aspect of the present invention, a path connection control method in a CDMA mobile communication system for determining a radio base station to establish a path for communication with a mobile terminal by a base station control unit, comprises:
first step of repeatedly inputting position information of the mobile terminal;
second step of deriving a current position, a traveling speed and a traveling direction of the mobile terminal on the basis of repeatedly input position information of the mobile terminal;
third step of providing a necessary path number map of predetermining necessary path number on the basis of a contour map, deriving necessary paths with taking information of current position, traveling speed and traveling direction of the mobile terminal and information from the necessary path number map and determining radio base stations to establish paths.
According to the fourth aspect of the present invention, a path connection control method in a CDMA mobile communication system for determining a radio base station to establish a path for communication with a mobile terminal by a base station control unit, comprises:
first step of repeatedly inputting position information of the mobile terminal;
second step of deriving current position, traveling speed and traveling direction of the mobile terminal based on repeatedly input position information of the mobile terminal, and predicting position, traveling speed and traveling direction of the mobile terminal in the near future;
third step of providing a necessary path number map of predetermining necessary path number on the basis of a contour map, deriving necessary paths in the near further with taking information of current position, traveling speed and traveling direction of the mobile terminal, predicted information of position, traveling speed and traveling direction of the mobile terminal in the near future and information from the necessary path number map and determining radio base stations to establish paths.
Preferably, the necessary path number map may be a necessary path number map based on a predicted traveling speed of the mobile terminal on the basis of the contour map. In the alternative, the necessary path number map may be a necessary path number map based on a predicted traveling direction variation ratio of the mobile terminal on the basis of the contour map. In a further alternative, necessary path number map may be a necessary path number map based on a predicted traveling speed variation ratio of the mobile terminal on the basis of the contour map. In a yet further alternative, necessary path number map may be a necessary path number map based on a predicted traveling speed of the mobile terminal, a necessary path number map based on a predicted traveling direction variation ratio of the mobile terminal on the basis of the contour map and a necessary path number map based on a predicted traveling speed variation ratio of the mobile terminal on the basis of the contour map.